Light modulator, light modulator method and smart glazing

ABSTRACT

Some embodiments are directed to a light modulator comprising transparent substrates, or a transparent substrate and a reflective or partially reflective substrate, multiple electrodes being applied to the substrates in a pattern across the substrate. A controller may apply an electric potential to the electrodes to obtain an electro-magnetic field between the electrodes providing electrophoretic movement of the particles towards or from an electrode.

FIELD

The presently disclosed subject matter relates to a light modulator, alight modulator method and a computer readable medium.

BACKGROUND

U.S. patent application Ser. No. 11/041,579, ‘Optically active glazing’,publication number US20050185104 A1, discloses known optically activeglazing, and is incorporated herein by reference.

The known system comprises two parallel plates, made from a transparent,or reflective or partially reflective material such as glass or aplastic material. The internal volume defined between the plates issubdivided into a plurality of small independent volumes or individualcells that are filled with a dielectric liquid. The liquid contains asuspension of particles of a dielectric material. The facing faces ofthe two plates carry electrodes facing each other. The electrodes areconnected to an electrical power supply associated with a control means.

The electrodes of each plate are formed by combs that are interleavedinto one another in pairs. The electrodes of two interleaved combs arecapable of taking up electrical voltages of polarities that areidentical or opposite. With a suitable voltage on the electrodes theparticles can be concentrated at different locations between theelectrodes to give the system either a transparent or an opaqueappearance.

A disadvantage of the known system is that the optical state of thesystem is unknown to the driver. The state can be approximated to someextent by keeping track of the amount of time some driving signal hasbeen applied, but the accuracy of this approach is low. Moreover, if thepanel was in an off-state, especially for some time, then the state ofthe panel is unknown.

SUMMARY

It would be advantageous to have an improved light modulator. A lightmodulator is provided that comprises at least one current sensingcircuit connected to an electrode on a substrate. The current sensingcircuit is configured to measure a current in the electrode to which itis connected. A controller determines driving signals for the electrodesat least from the current measured by the current sensing circuit toreach or maintain a target transparency or reflectivity. Interestingly,the location of the charged or chargeable particles in the lightmodulator changes both the optical properties of the light modulator aswell as the current in the electrodes. By measuring the latter,information is obtained about the former. In an embodiment, at least onecurrent sensing circuit is provided, e.g., for at least two electrodeson the same substrate, in particular, neighboring electrodes, or for twoopposite electrodes on opposite substrates. In an embodiment, allelectrodes have a corresponding current sensing circuit.

For example, current may be measured periodically in the electrode sothat the driving signal can be adapted as the transparency orreflectivity of the light modulator changes.

A light modulator is also known as an optical modulator. A lightmodulator provides a transparent or reflective panel of which thetransparency or reflectivity can be modified. In an embodiment, color orcolor intensity, etc., may be changed. A light modulator may be used ascover, e.g., a cover of a container, e.g., a closet, cabinet, and thelike. An especially advantageous application is in smart glazing. Smartglazing is also referred to as smart windows.

In embodiments, there are at least two electrodes on each substrate, butthere may be more than two electrodes. For example, at least threeelectrodes may be applied to at least one of the first substrate and thesecond substrate. For example, in an embodiment two electrodes may beapplied to a first substrate and three electrodes to a second substrate.In an embodiment, at least three electrodes are applied to eachsubstrate. At least two current sensing circuits may be applied to theat least three electrodes.

A system in which one substrate has at least two electrodes and theother has at least three electrodes has various advantages. For example,such a light modulator may be driven so that the so-called curtaineffect is reduced. The curtain effect happens during closing of thewindow (i.e., moving to a dark, opaque, or non-transparent state), inwhich it appears that a curtain is drawn between the electrodes. Thecurtain effect is a disadvantage, as it is visibly distracting initself, and it also increases diffraction. On a side with 3 electrodesthe electrodes can be closer together than on a side with 2 electrodes,e.g., below 50 micron, more preferably below 40 micron, e.g., 35 micron.This means that the electric field is stronger. Accordingly, closing isfaster and the curtain effect is reduced. With a 2+2 electrode panelmoving the electrodes closer together would lead to a reduced maximumtransparency or reflectivity, but when an additional electrode isavailable this is avoided. When opening some of the additionalelectrodes may be unused, so that there is little loss of maximumtransparency or reflectivity. Additional electrodes on a substrate,e.g., electrodes over two, may be configured not to attract particleswhen opening the panel, but to attract particles when closing the panel.

A further aspect of the invention is a building comprising a lightmodulator according to an embodiment. A further aspect of the inventionis a car comprising a light modulator according to an embodiment. Forexample, the car and/or building may comprise the light modulator and acontroller configured for controlling transparency or reflectivity ofthe light modulator by controlling voltage on electrodes of the lightmodulator. The controller being electrically connected or connectable tothe light modulator.

Light modulator and smart glazing are electronic devices, which may bedriven by a power source, e.g., under control of a controller. Forexample, the controller may instruct the power source to apply aparticular waveform to particular electrodes to achieve varioustransparency or reflectivity effects or the lack thereof.

An embodiment of the method may be implemented on a computer as acomputer implemented method, or in dedicated hardware, or in acombination of both. Executable code for an embodiment of the method maybe stored on a computer program product. Examples of computer programproducts include memory devices, optical storage devices, integratedcircuits, servers, online software, etc. Preferably, the computerprogram product comprises non-transitory program code stored on acomputer readable medium for performing an embodiment of the method whenthe program product is executed on a computer.

In an embodiment, the computer program comprises computer program codeadapted to perform all or part of the steps of an embodiment of themethod when the computer program is run on a computer. Preferably, thecomputer program is embodied on a computer readable medium.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details, aspects, and embodiments will be described, by way ofexample only, with reference to the drawings. Elements in the figuresare illustrated for simplicity and clarity and have not necessarily beendrawn to scale. In the figures, elements which correspond to elementsalready described may have the same reference numerals. In the drawings,

FIG. 1 schematically shows an example of an embodiment of a lightmodulator,

FIG. 2a schematically shows an example of an embodiment of a substrate,

FIG. 2b schematically shows an example of an embodiment of a substrate,

FIG. 3a schematically shows an example of an embodiment of a controller,

FIG. 3b schematically shows an example of an embodiment of a controller,

FIG. 4a schematically shows an example of an embodiment of a currentsensing circuit,

FIG. 4b schematically shows an example of an embodiment of a currentsensing circuit,

FIGS. 5a-5c schematically show an example of an embodiment of opening alight modulator,

FIGS. 6a and 6b schematically show an example of an embodiment ofclosing a light modulator,

FIG. 7 schematically shows an example of an embodiment of controlling alight modulator,

FIG. 8 schematically shows an example of an embodiment of controlling alight modulator,

FIG. 9a schematically shows an example of an embodiment of a lightmodulator,

FIG. 9b schematically shows an example of an embodiment of a lightmodulator,

FIG. 9c schematically shows an example of an embodiment of a car,

FIGS. 10a-10c schematically show an embodiment of a light modulator,

FIG. 11 schematically shows an example of an embodiment of a method ofcontrolling a light modulator,

FIG. 12a schematically shows a computer readable medium having awritable part comprising a computer program according to an embodiment,

FIG. 12b schematically shows a representation of a processor systemaccording to an embodiment.

LIST OF REFERENCE NUMERALS IN FIGS. 1, 2A-6B, 9A-10C, 12A-12B

The following list of references and abbreviations is provided forfacilitating the interpretation of the drawings and shall not beconstrued as limiting the claims.

-   10 a light modulator-   11 a first substrate-   12 a second substrate-   13, 13 a, 13 b electrodes-   14, 14 a, 14 b electrodes-   15 a fluid-   16 a controller-   30 particles-   20 a car-   21 a light modulator-   40 a light modulator-   41 a first substrate-   42 a second substrate-   43 a third substrate-   46 a controller-   100 a light modulator-   101-104 an electrode-   111, 112 a substrate-   113 an optical layer-   121-124 a driving line-   131-134 a current sensing circuit-   141-144 current sensing signal line-   150 a controller-   200 a substrate-   201 a first direction-   202 a second direction-   210 a first electrode-   211-213 a main-line-   220 a second electrode-   221-223 a main-line-   310 a controller-   330 a processor system-   340 a storage-   350 an interface-   361 a calibration unit-   370 a controlling unit-   371 a target transparency unit-   381 a driver-   382 a current sensing interface-   383 a sensor interface-   390 a light modulator panel-   391 a sensor-   401 a resistor-   411 a current sensing circuit-   422 a current signal-   431, 432 a buffer-   440 a programmable gain amplifier-   441 a current signal-   442 a gain signal-   511-514 a driving signal-   611-614 a driving signal-   1000 a computer readable medium-   1010 a writable part-   1020 a computer program-   1110 integrated circuit(s)-   1120 a processing unit-   1122 a memory-   1124 a dedicated integrated circuit-   1126 a communication element-   1130 an interconnect-   1140 a processor system

DETAILED DESCRIPTION OF EMBODIMENTS

While the presently disclosed subject matter is susceptible ofembodiment in many different forms, there are shown in the drawings andwill herein be described in detail one or more specific embodiments,with the understanding that the present disclosure is to be consideredas exemplary of the principles of the presently disclosed subject matterand not intended to limit it to the specific embodiments shown anddescribed.

In the following, for the sake of understanding, elements of embodimentsare described in operation. However, it will be apparent that therespective elements are arranged to perform the functions beingdescribed as performed by them. Further, the subject matter that ispresently disclosed is not limited to the embodiments only, but alsoincludes every other combination of features described herein or recitedin mutually different dependent claims.

FIG. 1 schematically shows an example of an embodiment of a lightmodulator 100.

Light modulator 100 comprises a first substrate 111 and a secondsubstrate 112. The first and second substrates arranged with inner sidesopposite to each other.

Multiple electrodes are applied to the inner side of each of the firstand second substrates. Shown in cross-section are electrodes 101 and 102on the inner side of substrate 111, and electrodes 103 and 104 on theinner side of substrate 112. Each of the multiple electrodes is arrangedin a pattern across the substrate. Examples of such patterns are givenbelow. In FIG. 1, two electrodes are shown on two substrates. A lightmodulator may have more than two substrates, and a substrate may havemore than two electrodes. Having more than two electrodes increasestransition speed, and improves driving of the light modulator.

Typically, a multiple-electrodes substrate is vertically aligned toanother multiple-electrodes substrate, but this is not necessary. Forexample, off-set placement may be used to reduce a parallax effect.There may be more substrates stacked above or below substrates 111 or112.

Between substrate 111 and 112 is an optical layer 113. The optical layercomprises a fluid in which particles are suspended. The particles areelectrically charged or chargeable, and are adapted to absorb or reflectlight. The reflection may be diffuse or specular reflection or inbetween. If there are multiple optical layers, e.g., using 3 or moresubstrates, then the particles in a different layer may have differentoptical properties, e.g., absorb or reflect at different wavelengths.

An electric potential, e.g., a voltage can be placed on the electrodesthrough a driving line. As shown in FIG. 1: Electrodes 101-104 areelectrically connected to driving lines 121-124 respectively. Thedriving lines 121-124 may be connected to a controller 150 configured toplace particular voltages on the driving lines. The electric potentialcauses electrophoretic movement of the particles which in turn affectsthe optical properties of light modulator 100, e.g., its transparency orreflectivity.

Many parameters of a light modulator may be varied to suit the needs ofthe application. For example, some applications need very dark, lesstransparent solutions while others need very transparent and less darksolutions. For some applications, energy efficiency is important, otherless so. Some applications want fast transitions, while others want highstability. These needs can often be met, e.g., by choosing the rightfluid, particles, electrode and substrate dimensions and so. Drivingsuch a variety of panels provides a challenge, which is also alleviatedwith current sensing. In an embodiment, the hardware of a singlecontroller design can be used with multiple panel types. Currentmeasuring allows the controller to adapt the driving signals to thepanel.

Light modulator 100 comprises at least one current sensing circuitconnected to an electrode on a substrate. A current sensing circuitmeasures current in the electrode to which it is connected. The amountof current passing through an electrode depends on the position of theparticles in the fluid with respect to the electrodes. Accordingly,measuring current in an electrode gives an indication of the number ofparticles near that electrode. The position of the particles gives anindication of the optical state of the light modulator. Accordingly,having only one circuit sensing circuit is preferable to having none,but to obtain more information from the panel, more circuit sensingcircuits can be placed. It is advantageous, to have at least two circuitsensing signals, e.g., in neighboring electrodes on the same substrateor in opposite electrodes on opposite substrate, since in this case acurrent between two electrodes can be computed from the measuredcurrents. Even more preferably, and as shown, a circuit sensing circuitis connected to each electrode of each substrate. As shown in FIG. 1:current sensing circuits 131-134 are connected to driving lines 121-124respectively. For example, the current sensing circuits may be part ofthe controller that drives the light module. The current sensing circuitcould be part of one or more of the substrates. For example, a lightpanel may comprise the current sensing circuits between the substrate,e.g., in the optical layer and electrically connected to the electrodes.

The current sensing circuits generate a current sensing signal which istransmitted to controller 150, e.g., over corresponding current sensingsignal lines 141-144. The controller 150 is configured to receive atleast one current sensing signal from the at least one current sensingcircuits. As shown in FIG. 1: the controller 150 is configured toreceive current sensing signal from current sensing circuits 131-134.The current sensing circuits may be part of controller 150, in whichcase, the current sensing signal lines may also be internal tocontroller 150. The controller is configured to determine an appropriatedriving signal for the electrodes from at least the received currentsensing signals.

The substrates, e.g., substrates 111-112, optical layers, e.g., layer113, the electrodes, e.g., electrodes 101-104, and possibly part of thedriving lines, e.g., lines 121-124 together constitute the panel part oflight modulator 100. Controller 150 may be integrated with the panel,but may also be connected through a wire, etc., with the panel.

FIG. 2a schematically shows an example of an embodiment of a substrate200. There are at least two electrodes arranged in a pattern across asurface of substrate 200. Shown in FIG. 2a are two electrodes on thesame surface: a first electrode 210 and a second electrode 220. Therecould be more than two electrodes on the same side of the substrate,e.g., to facilitate more fine-grained control. For example, multipleelectrodes may be used to facilitate a pixelated substrate, e.g., for apixelated light modulator. Below an embodiment with two electrodes isshown, but additional electrodes could be added to them, e.g., byreplicating similar structures next to each other.

First electrode 210 and second electrode 220 are applied to a same sideof the substrate. The two electrodes are arranged in a pattern acrossthe substrate. There could also be one, two or more electrodes on theother surface of substrate 200, e.g., to facilitate stacking of three ormore substrates. Applying electrodes to a substrate may be donelithographically, e.g., using a mask representing the electrodespattern. Electrodes may also be applied by embedding them in thesubstrate.

First electrode 210 and second electrode 220 each comprise a multiple ofmain-lines. As shown in FIG. 2a , first electrode 210 comprisesmain-lines 211, 212, and 213, and second electrode 220 comprisesmain-lines 221, 222 and 223. Typically, each electrode will comprisemore lines than three. The main-lines extend across the substrate. Themultiple of main-lines of the first and second electrode are arrangedalternatingly with respect to each other on the substrate. Themain-lines extend across the substrate in a first direction 201. Whenviewed in a second direction 202, the main-lines are encounteredalternately from different multiples, e.g., from the first and secondmultiple in the first and second electrode respectively. The first andsecond direction make an angle with each other, typically the angle issubstantially perpendicular. The first and second direction may each beparallel to a side of the substrate, but this is not necessary.

A motivating application for a substrate such as substrate 200 is insmart glazing, e.g., a light modulator, which may be applied in domestichousing, offices, green houses, cars, and the like. The level oftransparency or reflectivity of the smart glazing can be adaptedelectrically. For example, in smart glazing two substrates such assubstrate 200 would be stacked so that the sides on which the twoelectrodes are applied face each other. A fluid with particles isenclosed between the two substrates. In an embodiment, electrodes, e.g.,two or more electrodes are applied to one surface of each substrate.There could also be one, two or more electrodes on the other surface ofsubstrate 200, e.g., to facilitate stacking of three or more substrates.

Having two sets of alternating main-lines is sufficient to provideelectrically adaptable glazing; due to the alternating two sets theelectric field at any part of the substrate can be controlled as twoopposite electrodes border the part from two opposing sides.

FIG. 2b schematically shows two examples of embodiments of substrateswith electrode patterns according to an embodiment. The embodimentsshown in FIG. 2b are to scale, and can be extended to a full electrodepattern, e.g., following an interdigitated pattern. As an example, FIG.2b shows how the basic pattern of multiple main-lines can be extendedwith various features. For example, in FIG. 2b a pattern of branches isconnected to the main lines. Although such branches are not necessary,they reduce diffraction. Another possible extension is to include wavesin the main-lines.

FIG. 2b schematically shows an example of an embodiment of a substratearranged for two or for three electrodes. The left of FIG. 2b indicateswith the letters ‘a’ and ‘b’ which main lines belong to the sameelectrode. All lines marked ‘a’ are connected electrically, althoughthis is not shown in the detail of the electrode patterns shown in FIG.2b ; likewise for main-lines ‘b’. The right of FIG. 2b indicates withthe letters ‘a’, ‘b’ and ‘c’ which main lines belong to the sameelectrode. All lines marked with the same letter are connectedelectrically. Lines marked with a different letter are not connectedelectrically. Two of the substrates at the left of FIG. 5b may becombined into a 2+2 electrode light modulator. Two of the substrates atthe right of FIG. 5b may be combined into a 3+3 electrode lightmodulator

FIG. 3a schematically shows an example of an embodiment of a controller310. For example, the controller 310 of FIG. 3a may be used to control alight modulator, e.g., a light modulator as shown in FIG. 1. Controller310 may be used for controller 150. Controller 310 may comprise aprocessor system 330, a storage 340, and a communication interface 350.Storage 340 comprises local storage, e.g., a local hard drive orelectronic memory. Storage 340 may also comprise non-local storage,e.g., cloud storage. In the latter case, storage 340 may comprise astorage interface to the non-local storage.

Controller 310, e.g., communication interface 350, is configured tocommunicate with a light modulator for controlling the light modulator.The communication with the light modulator may comprise electric wiring,e.g., to drive the panel and to receive sensor signals, includingcurrent sensing signals. In controller 310, the communication interface350 may be used to send or receive analog data and/or digital data. Forexample, communication interface 350 may be configured for one or moreof the protocols: UART, SPI, I2C, CAN, etc.

For example, driving and sensing signals may be analog. For example,sensing signals may be digital, e.g., converted to digital. A drivingsignal could be digital and converted to actual voltage levels locallyat the light modulator.

Controller 310 may communicate with other systems, external storage,input devices, output devices, and/or one or more sensors over acomputer network. The computer network may be an internet, an intranet,a LAN, a WLAN, etc. The computer network may be the Internet. Thecontroller comprises a connection interface which is arranged tocommunicate outside of the device as needed. For example, the connectioninterface may comprise a connector, e.g., a wired connector, e.g., anEthernet connector, an optical connector, etc., or a wireless connector,e.g., an antenna, e.g., a 4G or 5G antenna.

The execution of controller 310 may be implemented in a processorsystem, e.g., one or more processor circuits, e.g., microprocessors,examples of which are shown herein. Controller 310 may comprise multipleprocessors, which may be distributed over different locations. Forexample, controller 310 may use cloud computing. Controller 310 may alsoor instead comprise a state machine.

FIG. 3b shows functional units that may be functional units of theprocessor system. For example, FIG. 3b may be used as a blueprint of apossible functional organization of the processor system. The processorcircuit(s) are not shown separate from the units in these figures. Forexample, the functional units shown in FIGS. 3b may be wholly orpartially implemented in computer instructions that are stored atcontroller 310, e.g., in an electronic memory of controller 310, and areexecutable by a microprocessor of controller 310. In hybrid embodiments,functional units are implemented partially in hardware, e.g., ascoprocessors, and partially in software stored and executed oncontroller 310.

FIG. 3b schematically shows an example of an embodiment of a controller310. Controller 310 is configured to control a light modulator panel390. Light modulator panel 390 comprises multiple substrates each withcorresponding multiple electrodes on the substrates and at least oneoptical layer enclosed between the substrates.

Light modulator panel 390 may be according to an embodiment, e.g., asdescribed in connection with FIG. 1 or FIGS. 9a-9c , etc. One or morecurrent sensing circuits may be comprised in controller 310; instead thecurrent sensing circuits may be comprised in light modulator panel 390.Preferably, light modulator panel 390 or controller 310 comprisesmultiple current sensing circuits, e.g., one for each electrode in lightmodulator panel 390. Also shown in FIG. 3b is an optional sensor 391cooperating with panel 390. Sensor 391 may comprise additional sensors,e.g., temperature or light sensors, as further explained herein.

Controller 310 comprises a driver 381. Driver 381 is configured to applyan electric potential, according to a driving signal, onto theelectrodes on the substrates of light modulator panel 390 to obtain anelectro-magnetic field between the electrodes. The electro-magneticfield provides electrophoretic movement of particles in light modulatorpanel 390 towards or from an electrode. For example, the driving signalmay directly be applied to the electrodes. For example, the drivingsignal may be indicative; for example, driver 381 may amplify thedriving signal before applying it to the electrodes. Driver 381 may beconnected to a power supply. Driver 381 could be local panel 390 insteadof comprised in controller 310.

Controller 310 comprises a current sensing interface 382 configured toreceive at least one current sensing signal from the at least onecurrent sensing circuit indicating current in the connected electrode.For example, current sensing interface 382 may receive current sensingsignals from all electrodes on all substrates. For example, whenconnected to the light modulator shown in FIG. 1, current interface 382may receive current sensing signals from electrodes 101-104. In anembodiment, the current sensing circuits are integrated with driver 381,and interface 382 may receive the current sensing signals from driver381. The current sensing signals may be analog or digital; They may beconverted from analog to digital, e.g., at interface 382, at the currentsensing circuits, or the like.

Optionally, controller 310 comprises a sensor interface 383 configuredto receive sensor signals from sensor 391. Sensor 391 may be arrangedon, or in, or near panel 390. Sensor 391 may be multiple sensors.

Controller 310 may optionally comprise a calibration unit 361. Forexample, calibration may be performed for panel 390 during manufacture,or may even be performed for another but similar panel. However, betterresults are obtained if calibration unit 361 is present in controller310. An advantage of having calibration unit 361 in controller 310 isthat re-calibration can be performed locally. This is an advantage,since the response of light modulator panel 390 may change over time.

Calibration unit 361 is configured to determine the response of lightmodulator panel 390 as it receives driving signals. For example,calibration unit 361 may drive panel 390 to a known state and measurethe current in the electrodes in the known state. A known state may beobtained by using sensors 391, e.g., a transparency sensor may bearranged on panel 390 to measure a transparency of the panel. However, aknown state can be obtained without having a transparency sensor, byapplying an electric potential to the electrodes to drive the lightmodulator to maximum transparency or to minimum transparency. Afterapplying the electric potential for a time interval, e.g., apre-determined time interval chosen to give panel 390 time to reachmaximum transparency or to reach minimum transparency, the currentsensing signals may be obtained from the multiple current sensingcircuits. As a result, current in the electrodes is obtained when panel390 is in a known state. Likewise, in another example, a reflectivitysensor may be arranged on panel 390 to measure a reflectivity of thepanel. After applying the electric potential for a time interval, e.g.,a pre-determined time interval chosen to give panel 390 time to reachmaximum reflectivity or to reach minimum reflectivity, the currentsensing signals may be obtained from the multiple current sensingcircuits

During use, after calibration, the drive signals may be determined fromcurrent sensing signals obtained in a use phase and the current sensingsignals obtained in an earlier calibration phase for a known state, andfrom, say, a target transparency or reflectivity.

Calibration values for the current in the electrodes when panel 390 isin a known state are advantageously obtained locally, e.g., after panel390 has been installed. For example, panel 390 may be smart glazing in abuilding or a car. Interestingly, calibration unit 361 allowsrecalibration. For example, controller 310 may be configured tocalibrate light panel 390 in various circumstances. For example, whenturning the light modulator on for the first time. For example, whenturning the light modulator on after being turned off for more than athreshold time. For example, when measuring out of range currents. Forexample, when a target transparency or reflectivity level is not reachedwithin a threshold time.

Controller 310 comprises a controlling unit 370. Controlling unit 370 isconfigured to determine driving signals for the electrodes from the atleast one current sensing signals and from a target transparency orreflectivity.

In an embodiment, the driving signals indicate an alternating current(AC) in the electrodes. The amplitude, frequency or bias of the drivingsignal may be different for different operations; for example, whenclosing, opening or measuring the panel 390, the amplitude, frequency orbias may differ.

Typically, the drive signals will indicate AC current, though thedriving signals could contain elements of DC bias, but nevertheless thedriving signal is preferably balanced to avoid corrosion of theelectrode material. For example, if panel 390 has been driven in DC fora first time interval, it is preferably driven with the oppositepolarity for a second time interval after that; the length of the firstand second interval or the voltages applied in them need not be thesame. To avoid corrosion of the electrodes the lengths of the timeintervals and the voltages applied in them are chosen so that loss andgain of electrode material of the electrodes is balanced. For example,in an exemplifying embodiment one may say drive using 1 volt DC for sometime; later the voltage may be 0.6 volt DC in the opposite polarity fora different amount of time. Balancing current is easier with AC drivingsignals.

Controlling unit 370 may be configured to determine a transparency orreflectivity level of the light modulator from the at least one currentsensing signals. From the current signals per electrode a current valuemay be computed between particular electrodes, e.g., as a differencebetween the measured current values. The computed current betweenelectrodes is indicative of the number of particles between them. If theparticles are mostly between electrodes on the same substrate then thepanel is opaque. If the particles are mostly between opposite electrodesof the two substrates and both substrates are transparent then the panelis transparent. If the particles are mostly between opposite electrodesof the two substrates and one of the substrates is reflective, then thepanel is reflective. Intermediate states can be obtained if one of thesubstrates is partially reflective.

For example, consider current measurements for electrodes 101-104 ofvalues I₁, I₂, I₃, I₄. The state of the panel may be computed as ƒ (I₁,I₂, I₃, I₄, h), wherein ƒ is a function and h is additional informationthat is available, e.g., temperature. In an embodiment multiplefunctions ƒ_(i) are computed. The latter may be used in case some of thefunction have less accuracy for some states, e.g., when the function isclose to zero, or a particular function may be used to drive to aparticular state or range of states.

Current between electrodes 101 and 102 may be computed as: I₁₂=abs(I₁−I₂). Current between electrodes 101 and 103 may be computed as:I₁₃=abs (I₁−I₃). Current may be also computed between groups of currentas the sum of I₁₂ and I₃₄ for example, or any other mathematicalcombinations.

When current between electrodes on the same substrate is high, e.g., ifI₁₂ is high, the panel is opaque. When current between electrodes onopposite substrates is high, e.g., if I₁₃ is high, the panel istransparent if both substrates are transparent; the panel is reflectiveif one of the substrates, e.g. the bottom substrate, is reflective.Intermediate states can be obtained if one of the substrates ispartially reflective. Either value, e.g., I₁₂ or I₁₃, may be used todetermine the optical state of panel 390. There is an advantage indetermining them both. When opening panel 390, e.g., when driving toincrease the transparency or reflectivity of panel 390, also known asvertical drive, one may primarily use I₁₃ since I₁₂ becomes increasinglysmall and less accurate as the panel opens. Likewise, when driving thepanel to decrease transparency or reflectivity, also known as horizontaldrive, one may primarily use I₁₂.

Note that one can also drive diagonally, which will cause the particlesto localize in the center. In this case the currents will equalize.Driving diagonally disperses the particles fast, and is a good way toclose the panel. Diagonal driving may be used, e.g., to turn off thepanel. One may compute the diagonal current as I₁₄=abs (I₁−I₄). In anembodiment, diagonal driving is used in combination with vertical orlateral driving and an electrode configuration the first substrate andthe second substrate each contain two electrodes. In an embodiment,diagonal driving is used in combination with an electrode configurationwherein at least three electrodes are applied to at least one of thefirst substrate and the second substrate.

The absolute functions (abs) facilitate easy computation of thecurrents, but are actually not necessary when care is taken to measurecurrent with the correct polarity. Current may be also computed betweengroups of current as the sum of I₁₂ and I₃₄ for example, or any othermathematical combinations.

Thus, the state of panel 390 may be determined from currents betweenelectrodes, which in turn can be computed from current on theelectrodes. The electrical currents between electrodes are dependent onthe location of the charged particles in the optical layer, e.g., in thedielectric fluid, while the locations of those particles directly impactthe transparency or reflectivity level of the light modulator. Bycomputing a vertical, horizontal, diagonal and/or combinations thereofof currents between electrodes an indication of the transparency orreflectivity state of panel 390 is obtained. In the examples give above,horizontal, vertical and diagonal current is computed. However, anyintermediate combination between these three directions can be taken.Using another combination of electrodes as a computed current has anadvantage when driving toward a transparency or reflectivity thatcorrespond to a similar combination of electrode currents, as thisincreases accuracy.

Computed currents between electrodes may be directly used to compute adriving signal. For example, controlling unit 370 may drive open panel390 so that I₁₃ achieves a particular value. Later the panel can bedriven towards the same value of I₁₃ again. For example, this may beused to ensure that equal transparency or reflectivity levels areachieved on different days. In this case calibration values are notstrictly needed.

However, when calibrated values are available, one can compute currentbetween electrodes in the known state and compute current for anyintermediate state and drive towards them. Moreover, calibration valuesallow driving towards the same transparency or reflectivity on differentoccasions, even if the response of the panel has changed, e.g., as aresult of aging, or a temperature change, etc.

For example, one may compute I₁₃ during calibration for two knownstates, e.g., fully dark and fully transparent, or fully dark and fullyreflective. To achieve a particular intermediate transparency orreflectivity, e.g., x % transparency or reflectivity, one may drivetoward a value of the current between electrodes, e.g., I₁₃, that liesat x % between the calibrated values. If calibration is only done forthe fully transparent state, one may assume that I₁₃ for the fullyclosed state is 0, likewise for the other values. However, calibratingwith two known states is preferable.

In other words, during calibration minimum and maximum values areobtained for the current between two electrodes. In a use phase, afterthe calibration phase, the current between the electrodes may be takenas an indication of the transparency or reflectivity of the panel. Forexample, going toward a dark state corresponds to this particular lowcurrent, going to a transparent or reflective state to this highcurrent, etc. A grey scale may be used when driving towards anintermediate current. A target transparency or reflectivity, e.g., atarget percentage, may be translated to a target current betweenparticular electrodes.

To establish the particular voltages, or maximum amplitudes for AC, aknown dynamic feedback control algorithm may be used, e.g., a closedloop algorithm known from control theory. For example, the controllermay repeat the following cycle

-   -   1. Translate a target transparency or reflectivity to a target        current between electrodes, by interpolating between calibrated        currents,    -   2. Apply a drive signal to electrodes in panel 390, for a time        interval    -   3. Measure current in electrodes using current sensing circuits    -   4. Compute currents between electrodes, e.g., horizontal and/or        vertical current    -   5. Compare computed currents with a target current, modify the        drive signal according to a dynamic feedback algorithm, and go        to number 2.

If the above algorithm is applied to currents computed from calibrationvalues, then the above algorithm will cause panel 390 to be driventowards the calibrated state, e.g., fully transparent, fully reflectiveor fully opaque. However, if the above algorithm is applied to currentsthat are intermediate between calibrated currents, then the abovealgorithm will cause panel 390 to be driven towards a state that isintermediate between the calibration states, e.g., intermediate betweenfully transparent, fully reflective or fully opaque.

The driving signal may be varied along multiple dimensions. A typicalchoice is voltage, e.g., peak voltage, but other elements that can bevaried in addition or instead are duty cycle, bias, waveform shape or ACfrequency. For example, using duty cycle may be advantageous for thepower consumption of the device. Another example is by using frequency,also the transition time between two intermediate device states may beaffected. The driving may also include the subsequent drive of multiplesegments to create subsequent electric field orientations.

Driving a panel 390 as in an embodiment will typically apply differentdriving signals to different electrodes. Accordingly, manufacturingvariations in the electrodes are taken into account. For example, givenany three electrodes, then the drive signal may be different for them.

In a variation of the above algorithm, the electrodes that are used tocompute a target current and drive towards it, is selected from thedirection in which the panel is driven, or likely driven. For example,to use I₁₃ for vertical drive and I₁₂ for horizontal drive, etc. One mayeven use a computed current, say, I′, that is specific for a particulartransparency or reflectivity. For example, panel 390 may first be driventowards a desired state using the known calibration states, after which,I′ may be computed. In future the I′ value may be used for driving. TheI′ value may be a linear combination of measured currents.

In an embodiment, more than two calibration states are used, e.g., morestates than fully dark and fully transparent or fully reflective. Thismay be done using a transparency or reflectivity sensor. For example,panel 390 may be driven to various states between fully dark and fullytransparent, the transparency may be measured with the transparencysensor and currents in the electrodes may be measured. Likewise, inanother example, panel 390 may be driven to various states between fullydark and fully reflective, the reflectivity may be measured with thereflectivity sensor and currents in the electrodes may be measured. Inan embodiment, a combination of a transparency sensor and a reflectivitysensor is applied. Accordingly, an even more accurate driving can beobtained. For example, one may compute the currents between electrodesat calibrates states and in use drive towards intermediate positions,represented by intermediate currents.

Controller 310 may comprise a target transparency unit 371 configured toset a target transparency. For example, target transparency may bedirectly set by a user, e.g., 75% grey. The target transparency isderived from a user input and/or sensor signal from a light sensor. Forexample, target transparency may be computed from a light sensor, e.g.,an ambient light sensor possibly together with an external light sensor.The light sensor may be in sensor 391; the light sensing signal may bereceived at interface 383. Target transparency may be expressed, say, asa percentage between minimal and maximal transparency. Targettransparency may be expressed as a target current. Light sensors areoptional; for example, target transparency may be directly taken fromuser input, from a schedule or the like.

If calibration is used, one may have two phases for a light modulator: acalibration phase followed by a use phase. The calibration phase maycomprise one or more cycles of driving toward a known state andmeasuring currents; two or four cycles. The calibration phase may alsocomprise measuring sensor values. The use phase may comprise multiplecycles of a driving part in which the panel is driven toward a targettransparency or reflectivity, and a measuring part in which currentsand/or other sensor values are measured. Instead of driving towards atarget transparency or reflectivity, the panel may be maintained at atarget transparency or reflectivity.

To measure a current in an electrode accurately, controller 310, e.g.,controlling unit 370 or driving unit 381 may, temporarily drive allelectrodes with a measuring signal. For example, the measuring signalmay be the same for different measuring operations. For example, themeasuring signal may be a constant signal, and may be the same for allelectrodes, or at least for all electrodes connected to the same opticallayer.

The measuring signal is applied during a measuring duration. During themeasuring duration, the current sensing signals are received. When themeasuring duration is over, normal driving of the panel may resume; forexample, an electric potential may be applied to the electrodesaccording to the driving signal.

For example, the measuring signal may be an AC signal, with someparticular maximum amplitude. While the measuring signal is beingapplied, multiple measurement samples may be obtained, e.g., when themeasuring signal is at peak amplitude, e.g., peak maximum and/or peakminimum. In this way, multiple samples are obtained, which may beaveraged or summed or any other mathematical combination for increasedaccuracy. As an exemplifying example, the AC signal may be 15 volt, and10 samples may be taken at +15 volt and 10 samples at −15 volt. Thesenumbers depend on the particular applications and the size of the panel,etc. The number of samples could be more or less, say, a 100 or more orless, the voltage could be different, etc. In an example, the electricpotential is a constant AC signal, all electrodes being driven with theconstant AC signal simultaneously or consecutively to assess the currentduring the measuring duration on all electrodes. In another example, theelectric potential is varying AC signal, all electrodes being drivenwith the varying AC signal simultaneously or consecutively to assess thecurrent during the measuring duration on all electrodes. The frequencyof the measuring signal could be the same as a frequency used fordriving, but is not needed. For example, one could take 100 Hz or 50 Hz,and so on. Again, these are examples. Also for the measuring signal itis preferred that it is DC-neutral to avoid corrosion.

During the measuring the location of the particles may change as aresult of the voltages applied to the electrodes. By keeping themeasuring duration short and/or the measuring amplitude low, this can beavoided. An advantage of measuring at relatively high frequency, is thatmultiple samples may be obtained in a short amount of time. For example,less than 50 samples per measurement; for example, measuring frequencyof at least 50 Hz.

The peak amplitude during measuring may be lower than during driving. Asan example, measuring voltage may be 10 volt, while the driving may beat 20 volt. These are only example values though and depend on manychoices, and in particular on the size of the panel. A smaller measuringvoltage has the advantage that it will cause less of a disturbance inthe particle locations. This is not necessary, as peak amplitude duringmeasuring may be higher than during driving. During maintenance of atarget transparency or reflectivity or when nearing the targettransparency or reflectivity, driving voltage may be reduced so thatmeasuring amplitude may be relatively higher.

Preferably the measuring duration is quite short, to avoid changing thelocation of the particles. Also, the current may change during themeasurement, which is also avoided by keeping the measuring durationshort. How short the measuring duration should be, depends, e.g., on howfast the particles move in the fluid. In an embodiment, measurementduration is less than, say, 100 ms, e.g., preferably less than 20 ms,e.g., 16 ms. Using more advanced current sensing circuits, the currentsensing duration may be considerably reduced, e.g., below 1 ms.

The measurement may be repeated after a certain amount of time passed.How often to repeat the measurement depends on the many factors. Forexample, for an optical layer with high stability, which has achievedits desired transparency or reflectivity, the measurement may berepeated after hours. For a faster optical layer, especially duringdriving towards a target transparency or reflectivity, the measurementsmay be repeated more often, e.g., once every 100 ms. In an embodiment,driving or maintaining takes at least 5 times longer than measuring.

Interestingly, after the measuring signal a counter drive signal may beapplied to correct for the distortion caused by the measuring. This isnot needed, as the normal driving will also correct the location of theparticles, but this feature can decrease possible distortion frommeasuring. For example, if the measuring signal has a lower potentialcompared to the one currently used to achieve a transparent state atequivalent frequency, after measuring the driving signal potential canbe amplified to compensate for the lower measurement signal appliedbefore.

In the use-phase, the controller is configured to measure the current inthe electrodes periodically. The frequency of measuring depends on theapplication, whether the panel has reached a desired target transparencyor reflectivity and is kept at this state or is actively driven towardsthe target transparency or reflectivity. For example, measuring could beonce every 100 ms, once every second. However, for a slow optical layerand a panel that is being maintained, the measuring may be much lessfrequent, e.g., at little as once an hour.

When the target transparency or reflectivity of the light modulator isreached or is within a threshold of the target transparency orreflectivity, the controlling unit may reduce an amplitude or duty cycleof the electric potential applied to the electrodes, and/or change acurrent measuring periodicity. For example, measuring periodicity maytemporarily be increased while the energy in the driving is reduced,e.g., when nearing the target. This has the advantage of reducingovershoot.

Various additional sensors 391 may be installed on, in or near panel390. For example, one or more temperature sensors may be configured tomeasure at least one of an outside temperature, inside temperature, anda fluid temperature in the optical layer.

If the optical layer is warmer, the particles will move faster.Controlling unit 370 may adapt in various ways. For example, measuringthe current may be done more often, as panel 390 is likely to reactquicker to changes in the driving signal. Likewise, if the temperatureincreases the driving frequency may increase. In an embodiment, closingthe panel uses a lower AC frequency than opening the panel. The slowerfrequency may be increased if the temperature increases. Since the riskof corrosion damage in the electrode increases with temperature a morebalanced driving is important, which is achieved with a higherfrequency. The relation between temperature and measuring or drivingfrequency may be a function, or a look-up table, etc.

FIG. 4a schematically shows an example of an embodiment of a currentsensing circuit 411. Shown is the driving line 121 of electrode 101. Aresistor 401 is included into driving line 121. A current sensingcircuit 411 measures the voltage drop over resistor 401 as an indicatorof current through resistor 401. A current signal 422 is transmitted toa controller, e.g., controller 150, or controller 310, etc.

FIG. 4b schematically shows an example of an embodiment of a currentsensing circuit. Shown are buffers 431 and 432 connected on one end toeither side of resistor 401 and on the other to the input of aprogrammable gain amplifier 440. The buffers may be precisionrail-to-rail input output op amps, preferably with a low current bias.

Programmable gain amplifier 440 is configured to receive a gain signal442; in this case in the form of four bits, giving 16 different gainsettings. Programmable gain amplifier 440 produces as output a currentsignal, e.g., the voltage drop over resistor 401 as output 441. In thiscase, output 441 is a differential output—the difference between theoutput signal indicating current through resistor 401, this is notnecessary, though convenient. The current signal 441 may be transmittedto the controller.

In an embodiment, the current sensing circuit can measure the current ina wide range, e.g., between 10 nA and 100 mA. This is useful, say, ifthe controller is used for different types of panels. Different paneltypes and sizes have different currents. Moreover, as pointed out someof the currents can be become very small, during driving. This canovercome by switching to other currents between other electrodes, but isalso alleviated by a programmable gain. Gain may be used to configure acontroller for a different panel. Advantageously, the same hardware maybe reconfigured for a different type of panel.

The output 441 may be a voltage difference. For example, current can becomputed from the voltage difference, the resistor value R, the gain,and a voltage reference Vref. For example, in an embodiment I=(OutputVoltage difference)/(R*GAIN*Vref). The reference voltage may be relatedto a reference voltage of an analog-to-digital converter (ADC) of thecontroller.

FIGS. 5a, 5b and 5c schematically show an example of an embodiment ofopening a light modulator. Shown in FIGS. 5b and 5c are the drivingsignals; driving signal 511-514 correspond to electrodes 101-104. Shownin FIG. 5a are the field lines according to which the particles move.With AC driving the particles in the liquid of the optical layer willbounce between the 2 substrates.

FIGS. 6a and 6b schematically show an example of an embodiment ofclosing a light modulator. Shown in FIG. 6b are the driving signals;driving signal 611-614 correspond to electrodes 101-104. Shown in FIG.6a are the field lines according to which the particles move. With ACdriving the particles in the liquid of the optical layer will bouncebetween the two electrodes on the same substrate.

In the situation shown in FIGS. 5b and 6b , all maximum amplitudes forall electrodes are equal. In an embodiment, some signals will have asomewhat higher amplitude, while some may have a somewhat loweramplitude, an example of which is shown in FIG. 5c . Moreover, thedriving signals will change over time, e.g., as parameters such aslight, temperature or target transparency or reflectivity changes.Moreover, the driving signals may also change when the panel has reacheda particular target transparency or reflectivity and only needs tomaintain it.

FIG. 7 schematically shows an example of an embodiment of a method 700of controlling a light modulator.

In part 710 the system is calibrated. For example, calibration may bedone when the system is turned on for the first time, not used for along time or the system detects out of range values. For example, ameasured current outside the range seen during calibration. In part 720the current is measured for each electrode that is in the lightmodulator panel.

In part 730 inner and outer light levels are measured, e.g., using aninverse logarithmic scale to define the target transparency of the lightmodulator panel; for example, light sensors may be applied on both sidesof the panel. For example, for a window with smart glazing, light levelsmay be measured inside the room and light levels outside the room,outside the window.

In addition to light levels, a temperature sensor may measure theoutside temperature, the inside temperature and/or the liquidtemperature inside the panel.

The temperature of the liquid, can have an impact on the performance ofthe panel. For example, the driving frequency and the currentmeasurement interval may change. The current measurement interval is anamount of time after which the current measurements in part 720 arerepeated.

In part 740 the output towards the light modulator panel is computedfrom the measured currents, light levels and temperatures. For example,a gray scale table may be defined that the controller can use to definethe panel. These can be used as setpoints for a feedback algorithm. Thetable can also be used as a selection table that a user can select,e.g., with a device that is connected to the system. The user device maybe wired or wireless, e.g., a button, a mobile phone, etc. In part 750the electrodes are drive according to the computed output.

Typically, a drive signal is computed for each electrode of the panel.Moreover, different target transparencies or reflectivities ortransition between different transparencies or reflectivities may have adifferent driving signal. The driving signal may differ in voltage,frequency, duty cycle for each of the electrodes, to drive toward thetarget transparency or reflectivity.

In part 760, it may be detected that new input is received, e.g., a newtarget transparency, or desired ambient light level from a user, or newsensor values, e.g., from light or temperature sensors. In part 770 itis determined if a new calibration is needed, or preferred, e.g., out ofrange values are detected. Out of range values could be a largetemperature change, say, over a threshold, a target transparency orreflectivity level not reached in time, etc.

If the panel is not driven, the system can go to a sleep mode. Theembodiment of FIG. 7 is an example, and can be varied in many ways, asalso pointed out herein. For example, the use of light sensor or the useof temperature sensors is optional. For example, instead of AC signals,balanced DC driving may be used, etc.

FIG. 8 schematically shows an example of an embodiment of a controllingmethod 800 for a light modulator panel. Controlling 800 comprises

Calibrating 810 comprising measuring current in the electrodes in onemore known states of the panel. Calibrating 810 may comprise determiningadditional parameters, for example, determining the maximum and minimumvalues of the panel performance, positive, negative and referencevoltages, temperature offset, light offset, grayscale selection offset,user input offset, etc. Calibrating can be done in factory before use,but can also or instead be done in the field at the customer.Calibration can be repeated, in whole or in part, when the system isturned on, rebooted, reset, timed-out, periodically, etc.

Obtaining sensor values 820. For example, obtaining sensor values maycomprise obtaining outside temperature, room temperature and insideoptical layer temperature. The temperature of the optical layer has animpact on the status of the panel. Measuring the temperature of theoptical layer allows the control algorithm to react to temperature.Sensor values may also include outside ambient light and room ambientlight. For example, this may be used to keep room ambient light stable.

Setting a target transparency 830. Target transparency may be computedfrom a room ambient light level. It may also be directly set by a userthrough a user interface.

Driving the panel 840. The panel may be driven for some time. In thefirst iteration, this may be an initial driving signal. The initialdriving signal may be a default driving signal. The initial drivingsignal may depend on a computed actual transparency level.

Measuring current 850. After driving for some time, the currents in theelectrode may be measured. This may comprise setting a measuring signalon the electrodes. Measuring current 850 may be interchanged withdriving 840.

Adapting the driving signal 860. A driving algorithm, e.g., a controlalgorithm such as a closed loop feedback algorithm may modify thedriving signal so that the measured current of part 850 will convergetowards currents computed to correspond to the target transparency. Thecomputed current can be obtained by interpolating current measuredduring calibration.

An exemplary embodiment of a light modulator is shown below.

FIG. 9a schematically shows an embodiment of a light modulator 10, whichmay be applied in smart glazing.

Reference is made to patent application PCT/EP2020/052379, which isincorporated herein by reference; this application comprisesadvantageous designs for a light modulator, which may be furtherimproved, e.g., by including electrodes and/or branches as explainedherein.

Light modulator 10 can be switched electronically between a transparentstate and a non-transparent state and vice versa, or between areflective state and a non-reflective state and vice versa. Lightmodulator 10 comprises a first substrate 11 and a second substrate 12arranged opposite to each other. On an inner-side of first substrate 11at least two electrodes are applied: shown are electrodes 13 a, 13 b.These at least two electrodes are together referred to as electrodes 13.On an inner-side of second substrate 12 at least two electrodes areapplied: shown are electrodes 14 a, 14 b. These at least two electrodesare together referred to as electrodes 14. Current sensing circuits maybe installed in electrodes 13 a and 13 b and 14 a and 14 b A fluid 15 isprovided in between the substrates. The fluid comprises particles 30,e.g., nanoparticles and/or microparticles, wherein the particles areelectrically charged or chargeable. The electrodes are arranged fordriving particles 30 to move towards or away from electrodes, dependingon the electric field applied. The optical properties, in particular thetransparency of the light modulator depends on the location of particles30 in the fluid. For example, a connection may be provided for applyingan electro-magnetic field to the electrodes. A controller 16 is shownconfigured to receive the currents sensing signals and to generatordriving signals for the electrodes 13 and 14.

In an example, substrate 11 and substrate 12 may be opticallytransparent, outside of the electrodes, typically >95% transparent atrelevant wavelengths, such as >99% transparent. The term “optical” mayrelate to wavelengths visible to a human eye (about 380 nm-about 750nm), where applicable, and may relate to a broader range of wavelengths,including infrared (about 750 nm-1 μm) and ultraviolet (about 10 nm-380nm), and sub-selections thereof, where applicable. In an exemplaryembodiment of the light modulator a substrate material is selected fromglass and polymer.

In another example, one substrate, such as a bottom substrate 12, may bereflective or partially reflective, while the top substrate 11 istransparent. The optical properties, in particular the reflectivity ofthe light modulator depends on the location of particles 30 in thefluid. When the panel is in the open state (vertical drive), theparticles will mostly be located between opposite electrodes of the twosubstrates, such that incident light can pass through the transparenttop substrate and the optical layer relatively unhindered, and isreflected or partially reflected on the bottom substrate.

The distance between the first and second substrate is typically smallerthan 30 μm, such as 15 μm. In an exemplary embodiment of the lightmodulator a distance between the first and second substrate is smallerthan 500 μm, preferably smaller than 200 μm, preferably less than 100μm, even more preferably less than 50 μm, such as less than 30 μm.

In an example the modulator may be provided in a flexible polymer, andthe remainder of the device may be provided in glass. The glass may berigid glass or flexible glass. If required, a protection layer may beprovided on the substrate. If more than one color is provided, more thanone layer of flexible polymer may be provided. The polymer may bepolyethylene naphthalate (PEN), polyethylene terephthalate (PET)(optionally having a SiN layer), polyethylene (PE), etc. In a furtherexample the device may be provided in at least one flexible polymer. Assuch the modulator may be attached to any surface, such as by using anadhesive.

Particles 30 may be adapted to absorb light and therewith preventingcertain wavelengths from passing through. Particles 30 may reflectlight; for example, the reflecting may be specular, diffusive or inbetween. A particle may absorb some wavelengths, and reflect others.

In an exemplary embodiment of the light modulator a size of thenanoparticles is from 20-1000 nm, preferably 20-300 nm, more preferablysmaller than 200 nm. In an exemplary embodiment of the light modulatorthe nanoparticles/microparticles may comprise a coating on a pigment,and preferably comprising a core. In an exemplary embodiment of thelight modulator the coating of the particles is made from a materialselected from conducting and semi-conducting materials.

In an exemplary embodiment of the light modulator the particles areadapted to absorb light with a wavelength of 10 nm-1 mm, such as 400-800nm, 700 nm-1 μm, and 10-400 nm, and/or are adapted to absorb a part ofthe light with a wavelength-range falling within 10 nm-1 mm (filter),and combinations thereof.

In an exemplary embodiment of the light modulator the particles areelectrically charged or chargeable. For example, a charge on theparticles may be 0.1e to 10e per particle (5*10⁻⁷-0.1 C/m2). Suitableexamples of such particles include are provided, for example, in U.S.Pat. No. 4,680,103 A, which is incorporated herein by reference. Forexample, suitable materials for the particles include inorganicpigments, such as titanium dioxide, alumina, silica or mixtures thereof,usually about 0.1 micron to about 10 microns in size. The pigmentparticles are charged either positively or negatively.

In an exemplary embodiment of the light modulator the fluid is presentin an amount of 1-1000 g/m2, preferably 2-75 g/m2, more preferably 20-50g/m2, such as 30-40 g/m2. It is a big advantage that with the presentlayout much less fluid, and likewise particles, can be used.

In an exemplary embodiment of the light modulator the particles arepresent in an amount of 0.01-70 g/m2, preferably 0.02-10 g/m2, such as0.1-3 g/m2.

In an exemplary embodiment of the light modulator the particles have acolor selected from cyan, magenta, and yellow, and from black and white,and combinations thereof.

In an exemplary embodiment of the light modulator the fluid comprisesone or more of a surfactant, an emulsifier, a polar compound, and acompound capable of forming a hydrogen bond.

Fluid 15 may be an apolar fluid with a dielectric constant less than 15.In an exemplary embodiment of the light modulator the fluid has arelative permittivity εr of less than 100, preferably less than 10, suchas less than 5. In an exemplary embodiment of the light modulator, fluid15 has a dynamic viscosity of above 10 mPa·s.

Electrodes 13 a, 13 b and electrodes 14 a, 14 b are in fluidic contactwith the fluid. The fluid may be in direct contact the electrodes, orindirectly, e.g., the fluid may contact a second medium with theelectrode, such as through a porous layer. In an embodiment, theelectrodes cover about 1-30% of the substrate surface. In an embodiment,the electrodes comprise an electrically conducting material with a sheetresistance of less than 10000 Ohms per square (Ω/sq), preferable lessthan 100 Ω/sq, more preferably less than 10 Ω/sq. In an embodiment ofthe light modulator one or more of the electrodes comprise one or moremetals selected from copper, silver, gold, aluminum, graphene, titanium,indium, preferably copper. The electrodes may be in the form ofmicro-wires embedded in a polymer-based substrate; for example, coppermicro-wires.

A connection for applying an electro-magnetic field to the electrodes,wherein the applied electro-magnetic field to the electrodes providesmovement of the nano- and microparticles from a first electrode to asecond electrode and vice versa, A connection for applying anelectro-magnetic field to the electrodes may be provided. For example,in an exemplary embodiment of the light modulator an electrical currentis between −100-+100 ρA, preferably −30-+30 ρA, more preferably −25-+25ρA. For example, a power provider may be in electrical connection withthe at least two electrodes. The power provider may be adapted toprovide a waveform power. At least one of amplitude, frequency, andphase may be adaptable to provide different states in the lightmodulator. For example, the aspects of the power may be adapted by acontroller.

Light modulator 10 may comprise one or more pixels, typically amultitude of pixels, the pixel being a single optically switchableentity, which may vary in size. The substrates enclose a volume, whichmay be a pixel, at least partly. The present design allows for stackingto allow for more colors; e.g., for full color applications a stack oftwo or three modulators could provide most or all colors, respectively.The present device may comprise a driver circuit for changing appearanceof (individual) pixels by applying an electro-magnetic field. As suchalso the appearance of the light modulator, or one or more partsthereof, may be changed.

In an exemplary embodiment of the light modulator, the light modulatorcomprises less than a pixel per mm2. Having one or more pixels allowsthe light modulator to be controlled locally; this is advantageous forsome applications, but not necessary. For smart glazing a lightmodulator may be used with or without pixels. For example, applied insmart glazing, transparency or reflectivity may be controlled locally,e.g., to block a sun-patch without reducing transparency or reflectivityin the whole window.

In an exemplary embodiment of the light modulator substrates (11,12) arealigned, and/or electrodes (13,14) are aligned. For example, electrodes13 a, 13 b and electrodes 14 a, 14 b may be aligned to be opposite eachother. In aligned substrates, electrodes on different substrates fallbehind each other when viewed in a direction orthogonal to thesubstrates. When the light modulator is disassembled, and the substratesare both arranged with electrodes face-up, then the electrode patternsare each other's mirror image.

Aligning substrates may increase the maximum transparency orreflectivity of the light modulator, on the other hand when selecting alight modulator for more criteria than the range of transparency orreflectivity, etc., it may be better to not to align or not fully alignthe two substrates. Light modulators can be stacked. For example, twostacked light modulators can be made from three substrates, wherein themiddles one has electrodes on both its surfaces. In an embodiment of thelight modulator optionally at least one substrate 11,12 of a first lightmodulator is the same as a substrate 11,12 of at least one second lightmodulator. Also, for stacked modulators, alignment may increase maximumtransparency or reflectivity, but is may detrimental to otherconsiderations, e.g., diffractions.

FIG. 9b schematically shows an example of an embodiment of a lightmodulator 40. Light modulator 40 is similar to light modulator 10,except that it comprises multiple optical layers; in the example asshown two optical layers. There may be more than two optical layers.Each optical layer is arranged between two substrates. Light modulator40 can be regarded as a stack of two-substrate light modulators as inFIG. 9a . As shown, light modulator 40 comprises three substrates: firstsubstrate 41, second substrate 42 and third substrate 43. Betweensubstrates 41 and 42 is an optical layer, and between substrates 42 and43 is an optical layer. The optical layers may be similar to those inlight modulator 10. A controller 46 is configured to control electricalcurrent on the electrodes of the substrates. For example, in FIG. 9b ,controller 46 may be electrically connected to at least 4 times 2 equals8 electrodes.

Interestingly, the particles in the multiple optical layers may bedifferent so that the multiple layers may be used to control moreoptical properties of the light modulator. For example, particles indifferent optical layers may absorb or reflect at different wavelengths,e.g., may have a different color. This can be used to create differentcolors and/or different color intensities on the panel by controller 46.For example, a four-substrate panel may have three optical layers withdiffer color particles, e.g., cyan, yellow, and magenta respectively. Bycontrolling the transparency or reflectivity for the different colors awide color spectrum may be created.

The surfaces of the substrates that face another substrate may besupplied with two or more patterns, e.g., as in an embodiment. Forexample, the outer substrates 41 and 43 may receive electrodes only onan inner side, while the inner substrate, e.g., substrate 42, may haveelectrodes on both sides.

Substrates 41 and 42 may together be regarded as an embodiment of alight modulator. Likewise, substrates 42 and 43 may together be regardedas an embodiment of a light modulator.

FIG. 9c schematically shows an example of an embodiment of a car 20having smart glazing for windows 21. This is a particularly advantageousembodiment, since while driving the level of incident lighting canchange often and rapidly. Using smart glazing in a car has the advantagethat light levels can be maintained as a constant level by adjusting thetransparency of the car windows. Moreover, the improved driving improvessafety since the car windows obtain a more accurate transparency. Forexample, when windows are darkened, they are less likely to be darkenedtoo much, or vice versa. Car 20 may comprise a controller configured forcontrolling the transparency of windows 21.

The smart glazing can also be used in other glazing applications,especially, were the amount of incident light is variable, e.g.,buildings, offices, houses, green houses, skylights. Skylights arewindows arranged in the ceiling to allow sunlight to enter the room.

FIGS. 10a-10b schematically show a side view of an embodiment of a lightmodulator in use. Applying an electric field to the electrodes on thesubstrates causes an electrical force on the particles. Using thiseffect, the particles can be moved around and so different transparencyor reflectivity states can be caused in the light modulator. Acontroller may control the electric field, e.g., its amplitude,frequency, and phase. In an embodiment, the controller is connected toat least four electrodes: two for each substrate. But more electrodesmay be used and connected to the controller; for example, more than 2electrodes may be used for a substrate to enable more control of greylevels or obtaining specific optical patterns.

FIG. 10a shows the light modulator without an electric field beingapplied. No electric force is yet applied on particles 30 suspended influid 15, in FIG. 10 a.

In the configuration shown in FIG. 10a , a conducting electrode patternarranged on the top substrate is completely or substantially alignedwith a conducting electrode pattern on the bottom substrate such thatthe required electrode configuration is obtained. The conductingelectrode pattern may be deposited on a transparent, reflective orpartially reflective substrate, or may be embedded in a plasticsubstrate, etc.

Alignment between the top-electrode pattern and the bottom electrodepattern contributes to a wider range of achievable levels oftransparency or reflectivity. However, alignment is not needed, assimilar effects can be obtained without alignment. Without alignment, arange of transparency or reflectivity is likewise obtained.

Note that in these examples, reference is made to the top substrate andthe bottom substrate to refer to substrate that is higher or lower onthe page. The same substrates could also be referred to, e.g., as thefront substrate and back substrate, since in a glazing application, thesubstrates would be aligned vertically rather than horizontally.

FIG. 10b shows the light modulator wherein, say at an instance P1, apotential +V1 is applied to each electrode on the top substrate, while anegative voltage, say −V1, is applied to each electrode of the bottomsubstrate. Thus, in this case, the same positive potential is applied toall electrodes 13, and the same negative potential is applied toelectrodes 14. The difference in potential causes negatively chargedparticles to flow to the vicinity of the electrodes of the topsubstrate, where those particles will substantially align with the topelectrodes. If the solution contains positively charged particles theywill flow to the vicinity of the electrodes of the bottom substrate,where those particles will substantially align with the bottomelectrodes. As a result, if both the top and bottom substrate aretransparent, the transparency of light modulator 10 will increase.Likewise, if e.g. the top substrate is transparent and the bottomsubstrate is reflective, the reflectivity of light modulator 10 willincrease. A similar transparency or reflectivity can be achieved, whenin a second instance, P2, of the on-state, the voltages of the topelectrode and bottom electrode are reversed in contrast to the instanceof P1. In the instance P2, the voltage of each electrode on of the topsubstrate are now supplied with a negative potential −V1 while thevoltages of the aligned electrode of the bottom substrate are suppliedwith a positive potential. This state is similar to the state shown inFIG. 10b , but with top and bottom substrates reversed. Also, in thisconfiguration the transparency or reflectivity of light modulator 10 ishigh.

Similarly addressing electrodes 13 and 14, in case of high temporalchange from P1 to P2 and so on (AC signal), the particles will alignwithin the electric field lines between the electrodes (withoutnecessary reaching the electrodes location). As a result, if both thetop and bottom substrate are transparent, the transparency of lightmodulator 10 will increase. Likewise, if e.g. the top substrate istransparent and the bottom substrate is reflective, the reflectivity oflight modulator 10 will increase.

Interestingly, by switching consecutively between a positive potentialat electrodes at the top substrate, e.g., as shown as electrodes 13 inFIG. 10b (and a negative potential on electrodes 14), and a positivepotential at electrodes at the bottom substrate (and a negativepotential on electrodes 13), e.g., as shown as electrodes 14 in FIG. 10b, the transparency or reflectivity can be maintained, while decreasingcorrosion damage to the electrodes. This alternating electric field canbe achieved by applying alternating electric potentials to the top andbottom electrodes.

Applying a waveform is optional, but it is a useful measure to increasethe lifetime of the light modulator by reducing corrosion. Corrosion canform for example, when using copper electrodes, since, copper ionsdissolve in an ionic fluid at one substrate and flow to copper electrodeon the opposite substrate, where they deposit. By applying a waveform,the direction of copper ion transport is frequently reversed, thusreducing corrosion damage. Between the two instances P1 and P2 thecorrosion current between the two substrates is balanced orsubstantially, e.g., >95%, balanced, e.g., as corrosion rate of anelectrode of the top plate occurs there is a balancing deposition ofcopper on the bottom electrode between each instance of time, P1 andvice versa in instance P2. Therefore, the particles are transitioning ormigrating continuously between top and bottom electrode, and the lightmodulator or smart window is always in the on-state while the dynamicelectrolysis current between the top and bottom electrode is constantthus there is no or a negligible net loss of copper electrode materialon the top and bottom substrates.

FIG. 10c shows how a state of decreased transparency or reflectivity canbe obtained. An alternating voltage is applied on the same substrate.For example, in an embodiment a potential +V2 is applied a firstelectrode and the next immediate neighboring electrode has an oppositepotential −V2 etc., as shown in FIG. 10c . This can be obtained byapplying the potential +V2 to electrode 13 a and the opposite potential−V2 to electrode 13 b. On the opposite substrate the potential +V2 maybe applied to electrode 14 a and the opposite potential −V2 to electrode14 b. For example, the electrodes may be arranged so that the electrodeson the substrates are aligned; an electrode on the top substrate havingan opposite electrode on the bottom substrate, and vice versa. Forexample, to decrease transparency or reflectivity, the oppositeelectrode may receive the same potential, while neighboring electrodesreceive an opposite potential. An embodiment is shown in FIG. 10c ,wherein four electrodes are indicated with the reference numbers 13 a,13 b, 14 a and 14 b, and the rest of the electrodes continue toalternate.

By using this AC drive cycle between top and bottom substrates, diagonaland lateral electric fields are generated between the two substratesthereby causing haphazard diffusion of the particles thereby creatingthe closed state of the light modulator. As a result of thisconfiguration, the particles migrate diagonally and laterally betweenthe top and bottom substrate and diffusion of particles into the visibleaperture of the light modulator contributes to the closed, opaque stateof the light modulator.

As for the transparent state shown in FIG. 10b , a waveform may beapplied to the electrodes, e.g., so that electrodes that are shown inFIG. 10b with a positive potential become negative and vice versa. As inFIG. 10b applying a waveform, e.g., between electrodes 13 a and 13 b andbetween 14 a and 14 b reduces corrosion damage to the electrodes.

The AC drive cycle may be implemented by using an interdigitated lineconfiguration, e.g., combining the top and bottom electrodeconfiguration shown in plan view in FIG. 2a or 2 b

The extent to which transparency or reflectivity is increased ordecreased in FIGS. 10b and 10c depends on the electrical signalamplitudes (voltages), frequencies and bias differences. By varying theamplitude difference, the amount by which the transparency orreflectivity increases, respectively, decreases, is controlled. Forexample, a curve representing light transmission versus voltage may bedetermined, e.g., measured. To obtain a particular level of lighttransmission, e.g., a particular transparency, e.g., a particulargrey-scale level, the corresponding voltage, e.g., AC voltage may beapplied. By interpolating the signals for a transparent or for anon-transparent state, levels in between transparent and non-transparentmay be obtained. Likewise, a curve representing light reflection versusvoltage may be determined, e.g., measured. To obtain a particular levelof reflectivity, the corresponding voltage, e.g., AC voltage may beapplied. By interpolating the signals for a reflective or for anon-reflective state, levels in between reflective and non-reflectivemay be obtained.

FIG. 11 schematically shows an example of an embodiment of a method 900of controlling a light modulator according to an embodiment. The methodmay be computer implemented. The method comprises

receiving (910) at least one current sensing signal from the at leastone current sensing circuits indicating current in a correspondingelectrode,

determining (920) driving signals for the electrodes from the at leastone current sensing signals and from a target transparency,

transmitting (930) the driving signal to the light modulator forapplying an electric potential to the multiple electrodes according tothe driving signal to obtain an electro-magnetic field between themultiple electrodes, wherein the electro-magnetic field provideselectrophoretic movement of the particles towards or from one of themultiple electrodes.

Many different ways of executing the method are possible, as will beapparent to a person skilled in the art. For example, the order of thesteps can be performed in the shown order, but the order of the stepscan be varied or some steps may be executed in parallel. Moreover, inbetween steps other method steps may be inserted. The inserted steps mayrepresent refinements of the method such as described herein, or may beunrelated to the method. For example, some steps may be executed, atleast partially, in parallel. Moreover, a given step may not havefinished completely before a next step is started.

Embodiments of the method may be executed using software, whichcomprises instructions for causing a processor system to perform method900. Software may only include those steps taken by a particularsub-entity of the system. The software may be stored in a suitablestorage medium, such as a hard disk, a floppy, a memory, an opticaldisc, etc. The software may be sent as a signal along a wire, orwireless, or using a data network, e.g., the Internet. The software maybe made available for download and/or for remote usage on a server.Embodiments of the method may be executed using a bitstream arranged toconfigure programmable logic, e.g., a field-programmable gate array(FPGA), to perform the method.

It will be appreciated that the presently disclosed subject matter alsoextends to computer programs, particularly computer programs on or in acarrier, adapted for putting the presently disclosed subject matter intopractice. The program may be in the form of source code, object code, acode intermediate source, and object code such as partially compiledform, or in any other form suitable for use in the implementation of anembodiment of the method. An embodiment relating to a computer programproduct comprises computer executable instructions corresponding to eachof the processing steps of at least one of the methods set forth. Theseinstructions may be subdivided into subroutines and/or be stored in oneor more files that may be linked statically or dynamically. Anotherembodiment relating to a computer program product comprises computerexecutable instructions corresponding to each of the devices, unitsand/or parts of at least one of the systems and/or products set forth.

FIG. 12a shows a computer readable medium 1000 having a writable part1010 comprising a computer program 1020, the computer program 1020comprising instructions for causing a processor system to perform alight modulator method, according to an embodiment. The computer program1020 may be embodied on the computer readable medium 1000 as physicalmarks or by magnetization of the computer readable medium 1000. However,any other suitable embodiment is conceivable as well. Furthermore, itwill be appreciated that, although the computer readable medium 1000 isshown here as an optical disc, the computer readable medium 1000 may beany suitable computer readable medium, such as a hard disk, solid statememory, flash memory, etc., and may be non-recordable or recordable. Thecomputer program 1020 comprises instructions for causing a processorsystem to perform the light modulator method.

FIG. 12b shows in a schematic representation of a processor system 1140according to an embodiment of a controller for a light modulator. Theprocessor system comprises one or more integrated circuits 1110. Thearchitecture of the one or more integrated circuits 1110 isschematically shown in FIG. 12b . Circuit 1110 comprises a processingunit 1120, e.g., a CPU, for running computer program components toexecute a method according to an embodiment and/or implement its modulesor units. Circuit 1110 comprises a memory 1122 for storing programmingcode, data, etc. Part of memory 1122 may be read-only. Circuit 1110 maycomprise a communication element 1126, e.g., an antenna, connectors orboth, and the like. Circuit 1110 may comprise a dedicated integratedcircuit 1124 for performing part or all of the processing defined in themethod. Processor 1120, memory 1122, dedicated IC 1124 and communicationelement 1126 may be connected to each other via an interconnect 1130,say a bus. The processor system 1110 may be arranged for contact and/orcontact-less communication, using an antenna and/or connectors,respectively.

For example, in an embodiment, processor system 1140, e.g., the devicemay comprise a processor circuit and a memory circuit, the processorbeing arranged to execute software stored in the memory circuit. Forexample, the processor circuit may be an Intel Core i7 processor, ARMCortex-R8, etc. In an embodiment, the processor circuit may be ARMCortex M0. The memory circuit may be an ROM circuit, or a non-volatilememory, e.g., a flash memory. The memory circuit may be a volatilememory, e.g., an SRAM memory. In the latter case, the device maycomprise a non-volatile software interface, e.g., a hard drive, anetwork interface, etc., arranged for providing the software.

A controller for a light modulator, e.g., to control voltages applied toelectrodes may comprise a processor circuit, but may also or insteadcomprise a state machine.

It should be noted that the above-mentioned embodiments illustraterather than limit the presently disclosed subject matter, and that thoseskilled in the art will be able to design many alternative embodiments.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. Use of the verb ‘comprise’ and itsconjugations does not exclude the presence of elements or steps otherthan those stated in a claim. The article ‘a’ or ‘an’ preceding anelement does not exclude the presence of a plurality of such elements.Expressions such as “at least one of” when preceding a list of elementsrepresent a selection of all or of any subset of elements from the list.For example, the expression, “at least one of A, B, and C” should beunderstood as including only A, only B, only C, both A and B, both A andC, both B and C, or all of A, B, and C. The presently disclosed subjectmatter may be implemented by hardware comprising several distinctelements, and by a suitably programmed computer. In the device claimenumerating several parts, several of these parts may be embodied by oneand the same item of hardware. The mere fact that certain measures arerecited in mutually different dependent claims does not indicate that acombination of these measures cannot be used to advantage.

In the claims references in parentheses refer to reference signs indrawings of exemplifying embodiments or to formulas of embodiments, thusincreasing the intelligibility of the claim. These references shall notbe construed as limiting the claim.

The invention claimed is:
 1. An electrophoretic light modulatorcomprising: a smart glazing for a window, the smart glazing including: afirst substrate and a second substrate, the first and second substratesbeing arranged with inner sides opposite to each other, multipleelectrodes being applied to the inner side of each of the first andsecond substrates, each of the multiple electrodes being arranged in apattern across the substrate, wherein applying an electric potential tothe multiple electrodes results in an electro-magnetic field between themultiple electrodes, the multiple electrodes each comprising a multipleof main-lines extending across the substrate in a first direction, themultiple of main-lines of the multiple electrodes being arrangedalternatingly with respect to each other on the substrate; an opticallayer between the first and second substrates, the optical layercomprising a fluid comprising particles, wherein the particles areelectrically charged, and wherein the particles are adapted to absorb orreflect light, wherein the electro-magnetic field between the multipleelectrodes provides electrophoretic movement of the particles towards orfrom one of the multiple electrodes; at least one current sensingcircuit connected to one of the multiple electrodes, the current sensingcircuit being configured to measure a current in the electrode to whichit is connected while the electrode is driven with a measuring signalapplied temporarily during a measuring duration, wherein the measuringsignal is an AC signal with a frequency of at most 100 Hz; and acontroller comprising a processor system configured to receive at leastone current sensing signal during the measuring duration from the atleast one current sensing circuit indicating a current in the connectedelectrode, determine driving signals for the multiple electrodes fromthe at least one current sensing signals and from a target transparencyor reflectivity, and apply the electric potential to the multipleelectrodes according to the driving signals when the measuring durationis over.
 2. The electrophoretic light modulator as in claim 1, whereinthe driving signal is provided as an alternating current (AC) in themultiple electrodes such that a substantially balanced electrolysiscurrent is obtained.
 3. The electrophoretic light modulator as in claim1, wherein the driving signal is provided as a direct current (DC) inthe multiple electrodes, wherein the voltage is periodically reversed tosuch extent that a substantially balanced electrolysis current isobtained.
 4. The electrophoretic light modulator as in claim 1, whereinthe first substrate and the second substrate are transparent.
 5. Theelectrophoretic light modulator as in claim 1, wherein one of the firstand the second substrates is transparent and one of the first and secondsubstrates is reflective or partially reflective.
 6. The electrophoreticlight modulator as in claim 1, comprising multiple current sensingcircuits, each electrode being connected to a corresponding one of themultiple current sensing circuits.
 7. The electrophoretic lightmodulator as in claim 1, wherein the controller comprising the processorsystem is configured to determine a transparency or a reflectivity levelof the light modulator from the at least one current sensing signals. 8.The electrophoretic light modulator as in claim 1, wherein thecontroller comprising the processor system is configured to apply anelectric potential to at least one of the electrodes according to ameasuring potential during a measuring duration, receive the at leastone current sensing signal from the at least one current sensing circuitconnected to an electrode during the measuring duration, and apply anelectric potential to the electrodes according to a driving signal afterthe measuring duration.
 9. The electrophoretic light modulator as inclaim 8, wherein the electric potential is a constant AC signal, allelectrodes being driven with the constant AC signal simultaneously orconsecutively to assess the current during the measuring duration on allelectrodes.
 10. The electrophoretic light modulator as in claim 1,wherein the controller comprising the processor system is configured tomeasure the current in the electrode periodically.
 11. Theelectrophoretic light modulator as in claim 10, comprising a temperaturesensor configured to measure at least one of an outside temperature,inside temperature, and a fluid temperature in the optical layer, thecontroller comprising the processor system being configured to receive atemperature signal from the temperature sensor, the controllerdetermining a current measuring periodicity from the temperature signal.12. The electrophoretic light modulator as in claim 1, wherein thecontroller comprising the processor system is configured to determine adriving signal for each electrode, driving signals for at least three ofthe multiple electrodes on the first and second substrate beingdifferent, causing different electric potentials to be applied to atleast three electrodes at the same time.
 13. The electrophoretic lightmodulator as in claim 1, wherein the controller comprising the processorsystem is configured for performing a calibration of the lightmodulator, the calibration comprising applying an electric potential tothe multiple electrodes to drive the light modulator to maximumtransparency, and/or to minimum transparency, and/or to maximumreflectivity, and/or to minimum reflectivity, and receiving at least onecurrent sensing signal from the at least one current sensing circuitscorresponding to maximum transparency, and/or to minimum transparency,and/or to maximum reflectivity, and/or to minimum reflectivity.
 14. Theelectrophoretic light modulator as in claim 13, wherein in a use phaseafter calibration, the driving signal is determined from at least onecurrent sensing signal obtained in the use phase, from the at least onecurrent sensing signals obtained in the calibration and from a targettransparency or reflectivity.
 15. The electrophoretic light modulator asin claim 13, wherein the controller comprising the processor system isconfigured to calibrate for at least one of: turning the light modulatoron for the first time, turning the light modulator on after being turnedoff for more than a threshold time, measuring out of range currents, atransparency or reflectivity level not being reached within a thresholdtime.
 16. The electrophoretic light modulator as in claim 1, whereindetermining a driving signal comprises determining one or more of avoltage, an AC frequency, a bias, a waveform shape and a duty cycle foreach of the electrodes.
 17. The electrophoretic light modulator as inclaim 1, wherein the target transparency or reflectivity is derived froma user input and/or sensor signal from a light sensor.
 18. Theelectrophoretic light modulator as in claim 1, wherein the controllercomprising the processor system is configured to, when the targettransparency or reflectivity of the light modulator is reached or iswithin a threshold of the target transparency or reflectivity, to reducean amplitude or duty cycle of the electric potential applied to theelectrodes, and/or change a current measuring periodicity.
 19. Theelectrophoretic light modulator as in claim 1, wherein the fluidcomprises a dielectric fluid.
 20. The electrophoretic light modulator asin claim 1, wherein the fluid comprises an apolar fluid with adielectric constant less than
 15. 21. The electrophoretic lightmodulator as in claim 1, wherein the particles include pigment particlescomprising an inorganic pigment.
 22. The electrophoretic light modulatoras in claim 21, wherein the inorganic pigment comprises titaniumdioxide, alumina, silica or mixtures thereof.
 23. The electrophoreticlight modulator as in claim 21, wherein the pigment particles arecharged either positively or negatively.
 24. An electrophoretic lightmodulator method comprising: providing a light modulator comprising: asmart glazing for a window, the smart glazing comprising: a firstsubstrate and a second substrate, the first and second substrates beingarranged with inner sides opposite to each other, multiple electrodesbeing applied to the inner side of each of the first and secondsubstrates, each of the multiple electrodes being arranged in a patternacross the substrate, wherein applying an electric potential to themultiple electrodes results in an electro-magnetic field between themultiple electrodes, the multiple electrodes each comprising a multipleof main-lines extending across the substrate in a first direction, themultiple of main-lines of the multiple electrodes being arrangedalternatingly with respect to each other on the substrate; an opticallayer between the first and second substrates, the optical layercomprising a fluid comprising particles, wherein the particles areelectrically charged, and wherein the particles are adapted to absorb orreflect light, wherein the electro-magnetic field between the multipleelectrodes provides electrophoretic movement of the particles towards orfrom one of the multiple electrodes; at least one current sensingcircuit connected to one of the multiple electrodes, the current sensingcircuit being configured to measure a current in the electrode to whichit is connected while the electrode is driven with a measuring signalapplied temporarily during a measuring duration, wherein the measuringsignal is an AC signal with a frequency of at most 100 Hz; receiving atleast one current sensing signal from the at least one current sensingcircuits during the measuring duration indicating current in acorresponding electrode, determining driving signals for the electrodesfrom the at least one current sensing signals and from a targettransparency or reflectivity, and transmitting the driving signals tothe light modulator for applying an electric potential to the multipleelectrodes according to the driving signals when the measuring durationis over.
 25. A transitory or non-transitory computer readable mediumcomprising data representing instructions, which when executed by aprocessor system, cause the processor system to perform the methodaccording to claim 24.